Heretofore, in order to improve visibility of an image display device, it has been common to provide an antireflection stack such as an antireflection film on the image display surface. The antireflection stack is designed to reduce reflectance over the entire visible light wavelength range, and, for example, one having a high refractive index oxide layer and a low refractive index oxide layer stacked alternately on a transparent substrate, has been known. The number of such high refractive index oxide layers and low refractive index oxide layers to be stacked, is not necessarily limited, but, it is usually about 4 layers as a total number of the high refractive index oxide layers and low refractive index oxide layers, from the viewpoint of the productivity, etc. (e.g. Patent Document 1).
The antireflection stack is required to have, in addition to the low reflectance, abrasion resistance, water resistance, fouling resistance, etc. Further, in order to improve the external appearance of e.g. an image display device having an antireflection stack mounted, the antireflection stack is required to be such that the reflected color has a moderate chromatic color, and a change in the reflected color due to a change in the angle of incidence of light, i.e. so-called multicolorization, is suppressed. Namely, it is required that when viewed from the front, the reflected color has a moderate chromatic color which is not excessively bluish, and when viewed obliquely at an angle, the reflected color has e.g. a white color which is not excessively reddish.
As a stack whereby the reflected color has a moderate chromatic color and a multicolorization is suppressed, such one is, for example, known that comprises a first oxide layer, a second oxide layer and a third oxide layer formed on a substrate, wherein the first oxide layer has a refractive index of from 1.74 to 1.88 and a thickness of from 45 to 65 nm, the second oxide layer has a refractive index of from 1.9 to 2.1 and a thickness of from 90 to 110 nm, and the third oxide layer has a refractive index of at most 1.48 and a thickness of from 80 to 110 nm (e.g. Patent Document 2).